In the art of cinematography two methods are commonly used to take and project a series of images which gives the subjective impression of a continuously moving picture. The best known and most common method involves stopping a length of film in the correct position relative to the optical system of the camera whilst an image is exposed on the film. After exposure the film is moved on until the next vacant position on the film is available to be exposed and a further exposure is made thereon. The sequence is repeated until the whole film is exposed. Projection involves the reverse procedure in which the film is moved continuously through a projector but in the region of the light path through the optical system of the projector, the film is moved in a series of jerks which by appropriate alignment will allow the different exposed regions or frames as they are referred to, to be aligned momentarily in the optical path and projected. By using an appropriate shutter mechanism, the light is cut off during the pull down time so that only the series of images corresponding to the sequence of frames is projected onto the screen.
Further light loss results by the incorporation of further shuttering to increase the flicker rate and reduce its subjective effects.
In a less common method the film is moved continuously through a projector and one or more moving optical components operate so as to arrest the movement of the frame images so as to produce a stationary display on the screen with each image (or frame) displacing the last at a repetition rate determined by the speed of movement of the film. The compensator can be thought of as comprising a series of facets which move in synchronism with the film in such a way that by appropriate alignment of the film and the facets, one facet will register with each frame in turn and with synchronised movement. As one frame of the film passes beyond the alignment position with one facet, the next frame of the film aligns with the next facet and so on.